File belt sander

ABSTRACT

A belt sander for sanding a workpiece including a main housing, a motor having a motor shaft disposed within the main housing, a gear assembly driven by the motor shaft, and a drive assembly coupled to the gear assembly for driving a sanding belt. The drive assembly includes a hammer coupled to the motor shaft, an anvil configured to receive rotational impacts from the hammer, and a spring biasing the hammer towards the anvil. The drive assembly is configured to convert the continuous torque provided by the motor and gear assembly to intermittent applications of torque to the anvil. The sanding belt is coupled to the anvil, such that the sanding belt is intermittently driven by the drive assembly when an abrasive load between the sanding belt and a workpiece causes a reaction torque exerted on the anvil to exceed a biasing force of the spring.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to prior filed, co-pending U.S. Provisional Patent Application No. 63/173,089, filed on Apr. 9, 2021, the entire content of which are incorporated by reference herein.

FIELD OF THE INVENTION

The present invention relates to power tools, and in particular to portable file belt sanders.

BACKGROUND OF THE INVENTION

File belt sanders generally include an abrasive sanding belt that is driven in a continuous loop. Typically, there is a series of wheels that drive the sanding belt in a continuous loop, where the wheels are spaced apart to create lateral runs therebetween. At least one of the lateral runs or wheels can press the sanding belt against a workpiece to perform a sanding/filing operation.

SUMMARY OF THE INVENTION

In one embodiment, the invention provides, among other things, a belt sander for sanding a workpiece including a main housing, a motor having a motor shaft disposed within the main housing, a gear assembly driven by the motor shaft, and a drive assembly coupled to the gear assembly for driving a sanding belt. The drive assembly includes a hammer coupled to the motor shaft, an anvil configured to receive rotational impacts from the hammer, and a spring biasing the hammer towards the anvil. The drive assembly is configured to convert the continuous torque provided by the motor and gear assembly to intermittent applications of torque to the anvil. The sanding belt is coupled to the anvil, such that the sanding belt is intermittently driven by the drive assembly when an abrasive load between the sanding belt and a workpiece causes a reaction torque exerted on the anvil to exceed a biasing force of the spring.

In another embodiment, the invention provides, among other things, a belt sander for sanding a workpiece including a main housing, a motor having a motor shaft disposed within the main housing, a contact arm extending from and moveable relative to the main housing for driving a sanding belt, and a drive assembly disposed between the motor and the contact arm. The drive assembly includes a hammer driven by the motor shaft about a drive axis, an anvil configured to receive rotational impacts from the hammer and coupled to the sanding belt, and a spring biasing the hammer towards the anvil. The drive assembly is configured to convert the continuous torque provided by the motor to intermittent applications of torque to the anvil. The sanding belt is intermittently driven by the drive assembly when an abrasive load between the sanding belt and a workpiece causes a reaction torque exerted on the anvil to exceed a biasing force of the spring.

Other aspects of the invention will become apparent by consideration of the detailed description and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a file belt sander according to an embodiment of the invention.

FIG. 2 is an exploded view of the file belt sander of FIG. 1.

FIG. 3 is a cross-sectional view of a drive assembly of the file belt sander of FIG. 1, illustrating an anvil, a camshaft, and a hammer.

FIG. 4 is a perspective view of a portion of the drive assembly of FIG. 3, illustrating hammer lugs of the hammer engaged anvil lugs of the anvil.

FIG. 5 is an exploded perspective view of a portion of the drive assembly of FIG. 3, illustrating the anvil coupled to a drive wheel of a drive assembly.

Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways.

DETAILED DESCRIPTION

FIG. 1 illustrates a portable power tool, such as a file belt sander 10 (referred to hereinafter as sander 10), for sanding a workpiece. In the illustrated embodiment, the sander 10 includes a main housing 14, a grip 18 disposed on the main housing 14 used for handling and maneuvering the sander 10 relative to a workpiece, and a battery pack 22 for providing electrical power to the sander 10. The main housing 14 is comprised of a plurality of sub-housings (e.g., two clamshell halves, unibody housings, etc.) that are connected together with threaded fasteners (e.g., screws). In some embodiments, the sander 10 may also include a supplemental handle 26 that is selectively coupled to the sander 10 to provide additional support and stability during operation, as shown in FIG. 2.

With reference to FIGS. 1 and 2, the sander 10 further includes a motor 30 that is positioned within the main housing 14 and operable to drive a sanding belt 34. The motor 30 is an electric motor (e.g., a brushless DC electric motor, a brushed DC electric motor, etc.) capable of producing a rotational output through a drive shaft 38 which, in turn, provides a rotational input to a gear assembly 42 (FIG. 2). The battery pack 22 connects to the main housing 14 and provides electrical power to the motor 30 when a trigger 46 is depressed. Specifically, an electronic controller 48 is disposed within the main housing 14 and transmits electrical current to the motor 30 in response to a user actuating the trigger 46. In other embodiments, the sander 10 may include a power cord 50 (FIG. 2) for electrically connecting the motor 30 to a source of AC power. The trigger 46 is conveniently positioned adjacent the grip 18 to allow a user to maneuver and activate the sander 10 with a single hand. The motor 30 defines a motor axis 54 along which the drive shaft 38 rotates when the motor 30 is activated. In the illustrated embodiment, at least part of the gear assembly 42 is driven along a transmission axis 62 that is perpendicular to the motor axis 54. In other embodiments, the motor axis 54 and transmission axis 62 are coaxial.

With reference to FIG. 2, the sander 10 further incudes a gear case 66 affixed to the main housing 14, which houses the gear assembly 42. The gear assembly 42 includes a pinion 70 coupled to the drive shaft 38 and a spiral bevel gear 74 intermeshed with the pinion 70. The pinion 70 and the spiral bevel gear 74 are disposed within the gear case 66. The gear assembly 42 is supported within the gear case 66 by a plurality of bearings 78, 79, 80. For example, the bearing 78 supports the pinion 70 for rotation within the gear case 66, whereas the bearings 79, 80 support the spiral bevel gear 74 for rotation within the gear case 66. A drive assembly 82 is coupled to an output of the gear assembly 42. Specifically, the drive assembly 82 is coupled to the spiral bevel gear 74 to thereby receive the torque output of the gear assembly 42. Although the gear assembly 42 of the illustrated embodiment includes a single spiral gear set, in other embodiments, the gear assembly 42 may alternatively include one or more spur gear sets, one or more helical gear sets, one or more planetary gear sets, or other styles of transmissions that provide a speed reduction between the motor 30 and the drive assembly 82.

With reference to FIGS. 2 and 3, the spiral bevel gear 74 is coupled to a camshaft 86 of the drive assembly 82 such that the camshaft 86 co-rotates with the spiral bevel gear 74. Accordingly, rotation of the drive shaft 38 rotates the pinion 70, which then transmits rotational torque to the spiral bevel gear 74 and thereby rotates the camshaft 86. The drive assembly 82 further includes an anvil 90, extending from the gear case 66, to which the sanding belt 34 can be coupled for performing work on a workpiece, as explained in further detail below. The drive assembly 82 is configured to convert the continuous rotational force or torque provided by the motor 30 and gear assembly 42 to a striking rotational force or intermittent applications of torque to the anvil 90 when the reaction torque on the anvil 90 exceeds a certain threshold. The anvil 90 experiences a reaction torque from an abrasive load when the sanding belt 34 contacts a workpiece. In the illustrated embodiment of the sander 10, the drive assembly 82 includes the camshaft 86, a hammer 94 supported on and axially slidable relative to the camshaft 86, and the anvil 90.

With reference to FIGS. 3 and 4, the drive assembly 82 further includes a spring 98 biasing the hammer 94 toward the anvil 90 along a drive axis 102, and a thrust bearing 106 and a thrust washer 110 positioned between the spring 98 and the hammer 94. The thrust bearing 106 and the thrust washer 110 allow for the spring 98 and the camshaft 86 to continue to rotate relative to the hammer 94 after each impact strike when hammer lugs 114 (FIG. 4) engage with corresponding anvil lugs 118. The spring 98 allows the drive assembly 82 to transition between an engaged state, in which hammer lugs 114 of the hammer 94 are meshed with anvil lugs 118 of the anvil 90, and a disengaged state, in which the hammer lugs 114 are spaced away from the anvil lugs 118 in a direction parallel with the drive axis 102. When transitioning to the disengaged state, the hammer lugs 114 cam against the anvil lugs 118, causing the hammer 94 to retract away from the anvil 90 against the bias of the spring 98. This occurs when the reaction torque exerted on the anvil 90 (via engagement with a workpiece) exceeds the biasing force of the spring 98. The reaction torque experienced by the anvil 90 is caused by the abrasive load between the sanding belt 34 and the workpiece. That said, the drive assembly 82 is transitioned to the disengaged state when the abrasive load on the sanding belt 34 exceeds an abrasive load threshold.

The preload of the spring 98 can be adjusted by an adjustment mechanism 100, causing the spring to either be expanded or compressed. The abrasive load threshold increases if the spring 98 is compressed via the adjustment mechanism 100. On the other hand, the threshold decreases if the spring is expanded via the adjustment mechanism 100.

The camshaft 86 further includes cam grooves 122 in which corresponding cam balls 126 are received. The cam balls 126 are in driving engagement with the hammer 94. The cam balls 126 are capable of moving within the cam grooves 122, which allows for relative axial movement of the hammer 94 along the camshaft 86 between the engaged state and the disengaged state while the camshaft 86 continues to rotate. In other words, the cam balls 126 rotationally drive the hammer 94 with the camshaft 86 and enable the hammer 94 to translate axially while the camshaft 86 is rotated relative to the hammer 94. A bushing 130 is disposed within the gear case 66 to rotationally support the anvil 90.

With reference to FIG. 5, the illustrated anvil 90 includes a splined shaft 134 at its distal end for creating a positive engagement with a belt drive system 138 (FIG. 2) that drives the sanding belt 34, as described in further detail below. In other embodiments, the anvil 90 may include other geometries (e.g., hexagonal, square, and the like).

With reference to FIG. 2, the belt drive system 138 includes a drive wheel 142, a driven wheel 146 driven by the drive wheel 142 via the sanding belt 34, and a contact arm 150 disposed between the drive wheel 142 and the driven wheel 146. The drive wheel 142 has a splined bore 152 that mates with the splined shaft 134 of the anvil 90 (FIG. 5) to create a positive engagement therebetween. Various surfaces of the contact arm 150 can be used to press the sanding belt 34 against a workpiece during a sanding/filing operation. For example, in one embodiment, the contact arm 150 includes a platen 154 along which the sanding belt 34 slides, creating a flat, working surface that presses the sanding belt 34 against a workpiece. The driven wheel 146 is also capable of pressing the sanding belt 34 against a workpiece, creating a rounded, working surface. In other embodiments, the contact arm 150 is an offset contact arm 150′ that enables the sanding belt 34 to deform around or conform in shape to a workpiece during a sanding/filing operation since there is no surface that presses the sanding belt 34 against a workpiece. Also, the contact arm 150, 150′ can be set to various angles and positions relative to the main housing 14. Although not illustrated, in some embodiments, the drive wheel 142 and driven wheel 146 have teeth disposed on the outer periphery that intermesh with corresponding teeth on the inner periphery of the sanding belt 34 to provide a positive engagement therebetween, such that the drive wheel 142 is inhibited from sliding relative to the sanding belt 34.

With continued reference to FIG. 2, the drive wheel 142 is disposed adjacent the gear case 66 of the sander 10 and defines a drive wheel axis 158, whereas the driven wheel 146 is disposed at a distal end of the contact arm 150 and cantilevered outward away from the main housing 14. The driven wheel 146 defines a driven wheel axis 162. The drive wheel axis 158 and the driven wheel axis 162 are parallel. A tensioning mechanism 166 is coupled to the contact arm 150 and is capable of moving the driven wheel 146 between a retracted position, in which the sanding belt 34 may be removed from the sander 10, and an extended position, in which the sanding belt 34 is placed under tension and inhibited from being removed from the sander 10. Specifically, the driven wheel 146 moves toward the drive wheel 142 in the retracted position to allow the sanding belt 34—having a fixed, rigid circumference—to fit around the drive wheel 142, the driven wheel 146, and the contact arm 150.

In operation of the sander 10, an operator depresses the trigger 46 to activate the motor 30, which continuously drives the gear assembly 42 and the camshaft 86 via the drive shaft 38. As the camshaft 86 rotates, the cam balls 126 drive the hammer 94 to co-rotate with the camshaft 86, and the hammer lugs 114 engage, respectively, the anvil lugs 118 to rotatably drive the anvil 90 and the sanding belt 34 (FIG. 3). During operation, impacting occurs when the anvil 90 encounters a certain amount of resistance, e.g., a large amount of friction between the sanding belt 34 and a workpiece. Specifically, impacting occurs when the abrasive load (i.e., friction) between the sanding belt 34 and the workpiece causes the reaction torque exerted on the anvil 90 to exceed the biasing force of the spring 98.

At this point, rotation of the anvil 90 and hammer 94 slows or seizes intermittently between each impact, causing the drive wheel 142 and sanding belt 34 to also stop rotating momentarily. Specifically, as rotation of the anvil 90 and hammer 94 slows or seizes, the camshaft 86 continues to rotate relative to the hammer 94, imparting a rearward axial displacement to the hammer 94 via the cam balls 126 and the cam grooves 122 to retract the hammer 94 from the anvil 90 and slide the hammer 94 rearward along the camshaft 86 against the bias of the spring 98, transitioning the hammer lugs 114 and the anvil lugs 118 to the disengaged state. As the hammer 94 moves rearward, the spring 98 stores some of the rearward energy of the hammer 94 to provide a return mechanism for the hammer 94. After the hammer lugs 114 disengage the respective anvil lugs 118 and slide past one another, the camshaft 86 rotationally accelerates the hammer 94 and the spring 98 rebounds to push the hammer 94 forward, toward the anvil 90, until the hammer lugs 114 and the anvil lugs 118 are in the engaged state to cause another impact. During each impact, the anvil 90 causes the drive wheel 142 and the sanding belt 34 to rotate along with the anvil 90. This abrupt, intermittent movement of the drive wheel 142 allows the sanding belt 34 to gouge and rapidly sand/file a workpiece at a faster rate than a traditional, continuous drive sander. Impacting continues to occur so long as the reaction torque exerted on the anvil 90 exceeds the biasing force of the spring 98. The electronic controller 48 is capable of varying the rotational output speed of the motor 30 in response to the abrasive load threshold being exceeded and/or the extent to which the trigger 46 is depressed.

Although the sander 10 is illustrated as a file belt sander, in other embodiments, the sander 10 may be a reciprocating sander, an orbital sander, a palm sander, a traditional belt sander, or other type of sander.

Although the invention has been described in detail with reference to certain preferred embodiments, variations and modifications exist within the scope and spirit of one or more independent aspects of the invention as described.

Various features of the invention are set forth in the following claims. 

What is claimed is:
 1. A belt sander for sanding a workpiece, the belt sander comprising: a main housing; a motor having a motor shaft disposed within the main housing; a gear assembly driven by the motor shaft; and a drive assembly coupled to the gear assembly for driving a sanding belt, the drive assembly including a hammer coupled to the motor shaft, an anvil configured to receive rotational impacts from the hammer, and a spring biasing the hammer towards the anvil, wherein the drive assembly is configured to convert the continuous torque provided by the motor and the gear assembly to intermittent applications of torque to the anvil, and wherein the sanding belt is coupled to the anvil, such that the sanding belt is intermittently driven by the drive assembly when an abrasive load between the sanding belt and a workpiece causes a reaction torque exerted on the anvil to exceed a biasing force of the spring.
 2. The belt sander of claim 1, further comprising a belt drive system driven by the drive assembly, wherein the belt drive system includes a drive wheel that is driven by the anvil, a driven wheel that is driven by the drive wheel via the sanding belt, and a platen disposed between the drive wheel and the driven wheel.
 3. The belt sander of claim 2, wherein the sanding belt has teeth on the inner periphery to intermesh with corresponding teeth of the drive wheel that, in turn, is directly coupled to the anvil, such that a positive engagement is established from the anvil to the sanding belt.
 4. The belt sander of claim 3, wherein the driven wheel has teeth that intermesh with the teeth on the inner periphery of the sanding belt.
 5. The belt sander of claim 1, further comprising a camshaft that is directly driven by the gear assembly and drives the hammer.
 6. The belt sander of claim 1, further comprising hammer lugs disposed on the hammer that engage with anvil lugs disposed on the anvil.
 7. The belt sander of claim 6, wherein the drive assembly is capable of transitioning between an engaged state, in which the hammer lugs are meshed with the anvil lugs, and a disengaged state, in which the hammer lugs are no longer meshed with the anvil lugs.
 8. The belt sander of claim 7, wherein the hammer lugs cam against the anvil lugs, causing the hammer to retract away from the anvil against the bias of the spring when the reaction torque exerted on the anvil exceeds the biasing force of the spring.
 9. The belt sander of claim 7, further comprising a camshaft that is directly driven by the gear assembly and drives the hammer, wherein the camshaft includes cam grooves and cam balls that rotationally couple the hammer to the camshaft and allows for relative axial movement of the hammer relative to the camshaft between the engaged state and the disengaged state while the camshaft continues to rotate.
 10. The belt sander of claim 1, wherein the biasing force of the spring can be adjusted by an adjustment mechanism, allowing the spring to either be expanded or compressed.
 11. A belt sander for sanding a workpiece, the belt sander comprising: a main housing; a motor having a motor shaft disposed within the main housing; a contact arm extending from the main housing for driving a sanding belt, the contact arm is moveable relative to the main housing; and a drive assembly disposed between the motor and the contact arm and including a hammer driven by the motor shaft about a drive axis, an anvil configured to receive rotational impacts from the hammer and coupled to the sanding belt, and a spring biasing the hammer towards the anvil, wherein the drive assembly is configured to convert the continuous torque provided by the motor to intermittent applications of torque to the anvil, and wherein the sanding belt is intermittently driven by the drive assembly when an abrasive load between the sanding belt and a workpiece causes a reaction torque exerted on the anvil to exceed a biasing force of the spring.
 12. The belt sander of claim 11, further comprising a drive wheel that is coupled to the anvil and disposed at one end of the contact arm, a driven wheel that is driven by the drive wheel via the sanding belt and disposed at another end of the contact arm, and a platen disposed on the contact arm and between the drive wheel and the driven wheel.
 13. The belt sander of claim 12, wherein the drive wheel and the driven wheel both have teeth that intermesh with corresponding teeth on the inner periphery of the sanding belt, such that a positive engagement is established from the drive wheel to the sanding belt.
 14. The belt sander of claim 11, further comprising a camshaft that is driven by the motor and coupled to the hammer.
 15. The belt sander of claim 14, wherein the camshaft includes cam grooves and cam balls that are received within the cam grooves, wherein the cam balls rotationally fix the hammer to the camshaft while also enabling the hammer to translate relative to the camshaft along the drive axis.
 16. The belt sander of claim 11, further comprising hammer lugs disposed on the hammer that engage anvil lugs disposed on the anvil.
 17. The belt sander of claim 16, wherein the drive assembly is capable of transitioning between an engaged state, in which the hammer lugs are meshed with the anvil lugs, and a disengaged state, in which the hammer lugs are spaced away from the anvil lugs in a direction parallel with the drive axis.
 18. The belt sander of claim 17, wherein the hammer lugs cam against the anvil lugs, causing the hammer to retract away from the anvil against the bias of the spring when the reaction torque exerted on the anvil exceeds the biasing force of the spring.
 19. The belt sander of claim 11, wherein the biasing force of the spring can be adjusted by an adjustment mechanism, allowing the spring to either be expanded or compressed.
 20. The belt sander of claim 11, wherein the contact arm is pivotable relative to the main housing about the drive axis. 